The present invention relates to a cap for insulating series loop connections on bar wound armatures of electrical systems such as generators and, more particularly, to a cap assembly for providing series loop cooling and extended electrical creepage distances from loop to loop.
U.S. Pat. No. 5,633,543 and U.S. Pat. No. 5,652,469 describe ventilated cooling systems for rotating electrical machines, such as generators, which provide for end region cooling.
An exemplary reverse flow ventilation system of the type disclosed in U.S. Pat. No. 5,633,543, is illustrated by way of example in FIG. 1. More specifically, FIG. 1 shows a cross-section of one-half of a generator 10 (see axial center-line 12 and longitudinal center-line 14) having a conventional reverse flow ventilated cooling system. A portion 16 of the flow of cooling gases is directed to the rotor 18. The cooling gases are drawn through ventilation ducts 20 in the rotor by centrifugal forces created by the spinning rotor. As the gases flow through the rotor, heat in the rotor is transferred to the gases. The heated rotor gases exit the ducts 20 at the surface of the rotor into an air gap 22 between the rotor 18 and stator 24. Spinning fans 26 mounted at the ends of the rotor draw the heated gas through the gap 22 between the stator and rotor. The heated gas is directed by an external duct 28 to a heat exchanger 30 that cools the gas.
The stator 24 is cooled by ventilation flow paths that are separate from the flow path in the rotor. Cold gas 32 cooled by the heat exchanger 30 enters a plenum chamber 34 surrounding the stator 24. Because the end sections of the stator are closest to the rotor exhaust fans 26, cooling gas tends naturally to flow in greater volume near the ends of the stator than through ducts at the center of the stator. This potential unbalance in the flow of cooling gas through the stator has traditionally been compensated for by baffle chambers 36 that extend around outer surface 38 of the stator.
The cooled gas 32 passes through the baffle chambers 36 (or directly to the stator near the center of the stator) and into cooling gas intake ducts 40 defined between packets 42 of stator core laminations. As the gas flows radially inward through the stator, heat from the stator coils 44, 46 is transferred to the gas. The fans 26 draw the warmed gas from the stator, into the air gap 22 and out to the external duct 28 to the heat exchanger 30.
A portion of the cooled gas 32 from the heat exchanger 30 is exhausted from exhaust ports 48 in the ends of the plenum chamber 34 and flows around the stator to cool the stator end turns 50.
U.S. Pat. No. 5,142,182 describes an adjustable width cap for insulating the series loop on wound armatures in electrical systems. The molded cap is formed from two identical cap sections which are assembled to define a loop cap enclosure that is adjustable in width for receiving different sized series loops. To mechanically lock the cap sections to one another, potting resin is disposed within the cap section.
The provision of molded end caps as disclosed in U.S. Pat. No. 5,142,182 precludes the direct gas cooling of the solid series loops 50. Thus, heat generated thereby must be thermally conducted along a heat flow path from the electrical winding, through the molded cap to the cooling gas.